This invention generally relates to photoresist patterning and more particularly to a photoresist development method for achieving improved critical dimension uniformity (CDU) including improved wafer yield in a photoresist patterning process.
Since the introduction of semiconductor devices, the size of semiconductor devices has been continuously shrinking, resulting in smaller semiconductor chip size and increased device density. One of the limiting factors in the continuing evolution toward smaller device size and higher density has been the stringent requirements placed on photolithographic processes as line width and step heights have decreased for device features. As one way to overcome such limitations, various methods have been implemented to increase the resolution performance of photoresists and to increase critical dimension uniformity (CDU) in the photolithographic patterning process.
Typically a photoresist layer is applied to a semiconductor wafer surface, for example, by spin coating a resinous layer over the process surface followed by what is referred to as a xe2x80x98soft bakexe2x80x99 at about 90xc2x0 C. to drive off solvents and to impart structural stability to the photoresist layer. The photoresist layer is then aligned and exposed to activating light, for example ultraviolet light (e.g., less than about 400 nm wavelength) through a photomask to transfer the mask image to the photoresist layer. The photoresist then typically undergoes a post exposure baking (PEB) process at about 110xc2x0 C. to improve adhesion and structural stability and smooth out standing wave profiles in I-line photoresists and to initiate catalyzed photoresist reactions in chemically amplified photoresists. The temperature and time period of the PEB process can be critical to CD control of developed photoresist profiles. Temperatures must typically be controlled to within about 0.1xc2x0 C. to prevent CD variations due to undesirable photoresist chemical reactions.
Following the PEB, a development process is carried out, the development process being the most critical step in accurately reproducing the mask image in the photoresist layer. The soluble portions of the photoresist are dissolved by liquid development chemicals. Since the goal is to accurately control CD features (minimum geometry features) to meet specifications, the development process must be properly controlled to avoid achieve acceptable photoresist profiles. For example, for positive photoresists, for example diazonapthoquinone (DNQ) novolak I-line resists, a solution typically containing tetra-methyl ammonium hydroxide (TMAH) is used as the developer to dissolve the exposed portions the photoresist. The developer may be applied by a variety of methods including continuous spray development where the developer is sprayed onto a spinning wafer and static developing methods such as puddle development where a puddle of developer is formed on the wafer for a period of time to allow for resist dissolution. A number of factors including nozzle spray pattern, wafer rotation speed, developer volume, developer solution normality, developer temperature, and the method of applying the developer are all critical factors in achieving acceptable photoresist profiles.
For example, referring to FIG. 1 is shown exemplary cross sectional views of defective photoresist profiles that may be caused by improper development. For example shown in FIG. 1 is shown a series of conceptual photoresist profiles formed over substrate 10. For example, photoresist profile portion 12 represents underdevelopment of a patterned photoresist profile. Photoresist profile portion 14 represents an incompletely developed patterned photoresist profile. Photoresist profile portion 16 represents an acceptably developed patterned photoresist profile while photoresist profile portion 18 represents an overdeveloped photoresist profile.
For example, according to the prior art, conventional I-line photoresists and photolithographic patterning methods are typically used for patterning larger features, for example upper metal portions such as bonding pads or wide area trench lines having widths of greater than about 1 micron. According to the prior art static development methods such as puddle development have been used with conventional DNQ I-line photoresist to develop larger features.
One problem with the prior art method of developing conventional I-line photoresists according to static methods is that the within wafer and wafer to wafer CD uniformity is frequently unacceptable due to under-development, incomplete development and over-development over portions of the process wafer surface as conceptually represented in photoresist profiles 12, 14, and 18 shown in FIG. 1. For example, frequently a minimum volume of developer is used in puddle development to minimize wafer backside wetting. As a result, small variations in developer volume, for example, insufficient developer volume frequently lead to under-development or incomplete development over portions of the wafer or wafer to wafer non-uniformities. In addition the failure to use an adequate volume of developer leads to formation of a scum layer of residual dissolved photoresist adversely affecting subsequent processes.
There is therefore a need in the semiconductor manufacturing art to develop an improved developing method for photolithographic patterning processes to achieve improved CD uniformity both within wafer and wafer to wafer.
It is therefore an object of the invention to provide an improved developing method for photolithographic patterning processes including conventional I-line photoresist to achieve improved CD uniformity within wafer and wafer to wafer while overcoming other shortcomings of the prior art.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method for developing a photo-exposed photoresist layer to improve a critical dimension uniformity (CDU) for a semiconductor device manufacturing process.
In a first embodiment, the method includes providing a semiconductor process wafer having a process surface comprising a photoresist layer photo-exposed according to an exposure pattern; dispensing a predetermined amount of developer solution over a stationary semiconductor process wafer to form a film of developer solution covering the process surface; partially developing the exposed portions of the photoresist layer comprising maintaining the semiconductor process wafer in a stationary position for a predetermined time period; rotating the semiconductor process wafer for a predetermined period of time to remove a portion of the developer solution; and, repeating the steps of dispensing, partially developing, and rotating, for a predetermined number of repetition cycles to complete a photoresist development process.
These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures.